Under current practice, wallpaper hangers and like workmen, when mounting covering materials over a wall, usually trim the top and bottom margins thereof by means of a straight edge and a razor blade, the straight edge acting as a guide for movement of the blade along a desired line of cut. Lateral edges of the covering material are similarly cut, particularly at corners of the room. In still other developments, so-called margin trimmers, which in general comprise razor blade holders of one type or another, have been developed for use with a straight edge guide as well as wheel knife trimmers which are rolled along a desired line of cut with or without the use of a guiding straight edge. In still other instances, modified wheel knives having serrated edges on the knife wheel have been developed to provide a series of perforations through the wall covering material, weakening the same along a desired tear line.
In all such prior known systems, great difficulty is encountered particularly in cutting the wall materials at corner intersections, for example, at the intersection of two sidewalls and a ceiling; such being greatly compounded by the need to employ a straight edge guide as above mentioned. This is especially true when using a razor blade per se since it is most difficult to hold the blade in a proper cutting position in a corner intersection while holding the straight edge guide in proper position. Even with the use of so-called utility knives in which the blade point extends forwardly of the blade handle, similar difficulty is encountered in attempting to cut a straight trim line.
In addition to the above-noted problem, currently known trim or utility knives, in which provision is made for holding a razor or other cutting blade, employ time consuming and cumbersome means for securing the blade in cutting position. In most instances, it is necessary to disassemble the knife housing to expose a mounting socket for the blade which is held in position by a system of interlocking projections on the housing. Once the blade is mounted in the socket, re-assembly of the housing is required.